Alerting: Notification Policy states flapping between Active and Unprocessed despite stable Firing alerts

### What happened? When configuring Notification Policies with custom timing parameters (`group_wait`, `group_interval`, `repeat_interval`), I observed inconsistent notification state behavior independent of actual alert state changes. **Observed behavior:** I focused on alerts sharing identical alert state change histories (verified via History view). Despite **identical alert state** transitions, these alerts show different notification behaviors: - Some alerts show stable Notification states (remain "Active" without unexpected transitions) - Others with the exact same alert state history exhibit flapping Notification states: "Active" → "Unprocessed" → "Active" → "Unprocessed" (cycling every 30 seconds to a few minutes) - Strangely, the time periods displayed next to each notification state (indicating how long the notification has been in that state) remain unchanged despite the state flapping - The flapping bypasses configured timing intervals, resulting in more notifications being sent than intended **Possible root cause:** Multiple alerts within the same notification group, with identical alert state histories, behave differently in notification state management. This seems to be a notification policy state tracking issue, not an alert evaluation problem. ### What did you expect to happen? - All alerts within the same notification group sharing identical alert state histories should exhibit consistent notification state behavior - Notification states should transition predictably according to configured timing parameters (`group_wait`, `group_interval`, `repeat_interval`) - Once a notification is sent (state: "Active"), it should remain "Active" until the next scheduled notification event based on the configured intervals - Notifications should not flip to "Unprocessed" without an actual alert state change requiring re-evaluation - Sent notifications (e.g., emails) should adhere to the configured timing intervals, not be sent more frequently due to state flapp…